278 THE NORTHERN MICROSCOPIST. 
ee E 
of this or that theory, but the ordinary laws of geometrical optics 
which determine that, all other things being equal, one objective 
will receive and transmit a greater quantity of light than another, 
and therefore has the larger or smaller aperture, according as the 
diameter of the beam emerging from it is greater or smaller. 
(To be continued.) 

LETTERS TO THE EDITOR. 
APERTURES AND AMPLIFICATION. 
Epiror’s REMARKS.—We present our readers with a verbatim 
report of the proceedings of the last meeting of the Manchester 
Microscopical Society, and understanding a paper was to be read 
settling for ever the aperture question, we therefore sent a reporter 
to take down such a valuable contribution. It is not our intention to 
debate the matter in its present form. Doubtless Prof. Abbe and 
his colleagues will feel proud of possessing such support as 1s 
afforded by the reader of the paper in question—we feel bound 
however to confess, that so far, we have not been able to appreciate 
the importance of what has been advanced, nor do we see what 
propositions have been established. The reader was, no doubt, 
eager, like Goliath, for the fray, and if he wished his views to be 
widely circulated, we have aided him in this respect. 
Upon 274 may be found Professor Martin Duncan's address 
to the mem of the Royal Microscopical Society ; it is so clearly 
expressed that we commend it to the notice of members of all 
societies, both young and old. 

To the Editor of the Northern Microscopist. 
DEAR SIR, 
Referring to the Aperture Shutter, at the last meeting of 
the Manchester Microscopical Society, Mr. Miles described it as a 
scientific toy. Now, if we are so to describe every piece of 
apparatus which does not answer all our individual requirements, 
we shall very soon dispense with the whole of our Microscopic 
accessories. Take for instance the “ spot lens,” that simple and 
useful little instrument for producing such beautiful effects of dark- 
ground illumination of Pond-life, Polycistina, Mosses, &c., but, 
which for the majority of objects is entirely useless, and is seldom 
or never used in tracing out the life-history of vegetable or animal 
organisms. Again, take the Camera-lucida, for which we pay 
prices ranging from 6s. 6d. to £2 2s., but, which every micros- 


